How to choose measurement conditions when AA-1800 atomic absorption spectrometry is determined - Database & Sql Blog Articles

How to Choose Measurement Conditions for AA-1800 Atomic Absorption Spectrometry

Key words: atomic absorption spectrometry; measurement conditions; analysis instrument; AA-1800 The AA-1800 atomic absorption method is more precise than atomic emission spectroscopy due to several key factors. First, it uses a sharp line source and the resonance absorption line, which significantly reduces the number of absorption lines compared to emission lines. This minimizes spectral overlap and interference. Second, the method involves ground-state atoms, making it less sensitive to flame temperature variations. However, in practice, various types of interference can still occur, so it's important to understand their causes and how to eliminate them. In atomic absorption spectroscopy, there are four main types of interference: physical, chemical, spectral, and background. Choosing the right measurement conditions is crucial for accurate results. 1. **Selection of Analysis Line**: Typically, the resonance line of the element is used for higher sensitivity. However, if the sample has a high concentration, a non-resonant line may be chosen to avoid excessive absorbance values. Also, self-absorption and line interference should be considered during selection. 2. **Hollow Cathode Lamp Current**: The lamp’s performance depends on its current. Too low a current leads to unstable discharge and weak light output, while too high a current broadens the emission line, reducing sensitivity and shortening the lamp’s life. It's recommended to use about 1/2 to 2/3 of the maximum allowed current. The optimal current should be determined experimentally by observing changes in absorption values. 3. **Flame Selection and Adjustment**: The flame type plays a major role in atomization efficiency. For elements that form stable oxides, a high-temperature acetylene-nitrous oxide flame is preferred. For elements with wavelengths below 220 nm, a hydrogen-air flame is suitable. Once the flame type is selected, the gas-to-fuel ratio must be adjusted to achieve the best flame characteristics. A rich flame is used for elements that form stable oxides, while a lean or stoichiometric flame is better for unstable oxides. 4. **Burner Height**: Adjusting the burner height ensures that the light beam passes through the region with the highest free atom concentration, improving sensitivity. For example, for chromium, which forms stable oxides, increasing the flame oxidation potential decreases absorbance. For silver, which is less stable, absorbance increases with flame potential. For magnesium, absorbance increases with flame height until it peaks, then decreases. Therefore, careful adjustment is necessary during measurements. 5. **Slit Width**: The slit width affects the spectral bandwidth and radiation detection. It should be set to separate the absorption line from interfering lines. If interference occurs, absorbance drops immediately. The optimal slit width is the largest one that doesn’t cause this drop. Wider slits are often used in atomic absorption due to low line overlap, which increases light intensity and lowers detection limits. However, for elements with complex spectra, narrower slits are preferred. Experimentation is always recommended to determine the best setting.